As shown in FIG. 4, a dynamic microphone generally uses a vibrating plate formed with synthetic resin such as polyethylene or polyester. The vibrating plate includes a center dome 10 and a sub-dome 20 which connects and communicates with the outer circumference of the center dome 10 as to elastically supports the center dome. (see Japanese Patent Application Publication No.4-115696).
A voice coil 30 for generating electricity is installed on the center dome 10 with an adhesive or the like. The voice coil 30 is disposed in a magnetic gap (not shown) and the coil as well as the center dome 10 is vibrated by arriving sound waves in the magnetic gap so that the sound waves are converted to an electric signal.
Therefore, the center dome 10 undertakes an important role to increase a conversion efficiency and to improve a frequency response of the dynamic microphone. Especially, in order to obtain a good frequency response in high frequencies, the center dome 10, not only, should have a high mechanical intensity, but also, should mechanical-strongly bond the voice coil 30.
The vibrating plate 1 is driven by sound waves. If the mechanical intensity of the center dome 10 is low, a deformation of the center dome 10 generates a transfer loss against the voice coil 30. If an adhesive which bonds the voice coil 30 to the center dome 10 has a low hardness, another transfer loss occurs at the bonded portion between the dome and the coil.
As one of measures of strengthening the mechanical intensity of the center dome 10, it is known that the center dome 10 is formed to a double structure with a dome-shaped applying plate (sheet) applied to the center dome 10, and the transfer loss at the bonded portion between the center dome 10 and the voice coil 30 can be solved by using an adhesive having a high hardness after the adhesive has hardened.
However, since the double structure of the center dome needs the additional applying plate and an additional manufacturing step to apply the applying plate, it is not preferable regarding to a cost. When the adhesive having the high hardness after the adhesive has hardened is used to bond the vibrating plate 30 to the center dome 10, the bonded portion is non-resistant against a strong shock received from outside due to the high hardness of the adhesive, and it is another problem to occur that the bonded portion comes off easily.